Such hollow fiber arrangements are generally known. The hollow fiber arrangements are disposed in humidifiers, whereby an air stream is conducted inside the fibers and another air stream is conducted outside of the fibers. In this context, one air stream is laden with water vapor that at least partially passes through the fibers into the other air stream. A problematic aspect of hollow fiber arrangements is that the air stream conducted on the outside causes the fibers to cluster together in some places and to move away from each other in other places. As a result, the air circulates unevenly around the fibers and a uniform mass transfer is no longer ensured.